<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
    <style>
        .back{
            position: fixed;
            bottom: 0px;
            right: 0px;
        }
        .hide{
            display: none;
        }
    </style>
</head>
<body>

<div style="height: 2000px;"></div>

<div onclick="GoTop()" class="back hide">返回顶部</div>

<script src="jquery-2.1.4.js"></script>
<script type="text/javascript">

    function GoTop(){
        //返回顶部
        $(window).scrollTop(0);
    }

    $(function(){

        $(window).scroll(function(){
            //当滚动滑轮时，执行函数体

            //获取当前滑轮滚动的高度
            var top = $(window).scrollTop();

            if(top>100){
                //展示“返回顶部”
                $('.back').removeClass('hide');
            }else{
                //隐藏“返回顶部”
                $('.back').addClass('hide');
            }
        });
    });

</script>

</body>
</html>